We have studied the superconducting transition in niobium nanowires with niobium and graphene leads. When the current is injected through a graphene lead, we find a large enhancement of the resistance at the superconducting transition. This resistance anomaly is not caused by noise and does not depend on the magnetic field, but it depends strongly on the resistance of the graphene leads, which can be tuned by a back gate. We will discuss the possible origins of this phenomenon.

*This work was supported in part by the National Science Foundation under grant DMR-1663683.